Introverted Sensing deals primarily with recalling facts and details of past events. The Si user has a great memory and is able to recall experiences from the past with great accuracy. The Si user believes the past is a very good indicator of future events and uses it as a guideline when making decisions.
The ISFJ and ISTJ have Introverted Sensing as their primary function. The ESTJ and ESFJ have Si as their secondary function.
Introverted Sensing is very tradition and ritual oriented. They hold on to these traditions very closely and are the most active in their family when it comes to honoring them. For example, the Si user can become very sentimental around Thanksgiving and Christmas and expect all their family members to be there. They can also work very hard and performing the same role every year, whether it is carving the turkey, setting up the Christmas tree, or cooking for everyone. The Introverted Sensor sees these events as symbolic and meaningful and would feel a bit lost without them.
Introverted Sensors are also very consistent and hard working. They see the role they are in as their duty, and they take pride in performing it to the best of their ability. They tend to know all the facts and rules that their role or job entails and make sure to adhere to them. They tend to enjoy being in a predictable system with a steady paycheck that gives them job security. The Si user will strive to find a comfort zone to stay in and will do whatever they can to preserve it. Change and unpredictability is unsettling to the Introverted Sensor and can make them feel lost.
A problem that can occur with Introverted Sensing is that if it is relied upon to heavily, the person may never have new life experiences. They may just continue doing what they have always done. Without new experiences, how does the Si user know whether or not there is something out there that is more enjoyable?
The ISFJ and ESFJ would be wise to develop their Extraverted Feeling function. By going out into the world and just observing others emotions and behavior, they can get a better sense of how they can fit into different roles and allow new and meaningful people to enter their lives.
The ISTJ and ESTJ should develop their Extraverted Thinking to better understand the world and how they can organize it to get more of what they want. They can also come to a better understanding of where others are coming from, which could help them to accomplish their goals.
The INTP and INFP also have Introverted Sensing as their tertiary function. They can use this function to find and develop enjoyable routines in their life. They can use these routines and traditions to find comfort in a world that may be a bit challenging and chaotic to them. Introverted Sensing also has a high sense of nostalgia. The INFP and INTP may find themselves reconnecting with others they were close to in the past, as well as old hobbies.